1. Field of the Invention
This invention relates to a light-weight post hole digger and, more specifically, to a post hole digger having a traverse pivot point coupling two handle assemblies to each other, a blade assembly having two blade members, each blade member pivotally coupled to one handle assembly, and an offset pivot point coupling the two blade members to each other.
2. Background Information
A post hole digger is structured to dig a hole having a generally narrow cross-sectional area relative to the depth of the hole. The hole was typically dug in a compacted particulate or granulated material, hereinafter “the ground.” The material removed from the hole shall be referred to as “the dirt.” The dirt was, typically, a loose granulate material. Preferably, the post hole had a greater cross-sectional area than a post that was inserted therein. A portion of the loose dirt, or another material such as concrete, was then reinserted into the annulus, or gap, between the post and the ground. Because the compacted ground was more firm than the loose dirt, and therefore provided better support for the post, it was desirable to have as narrow of a hole as possible. Thus, one factor in the design of a post hole digger was the span of the post hole digger during insertion and, especially, during removal. Keeping in mind that a worker must cyclically operate a manual post hole digger, other important factors related to how a worker interacted with the tool. Such factors included, but were not limited to, the weight of the post hole digger, the force required to operate the post hole digger, the amount of dirt collected during each cycle, and the range of motion through which a worker must act during each cycle. For example, a post hole digger with longer handles typically had a longer lever arm and, therefore, provided a greater closing force on the blade members; however, the handles may not be too long as the tool could be too heavy to lift repeatedly and/or too unwieldy to use comfortably.
Manual post hole diggers generally had two elongated handles with each handle having an upper hand grip portion and a blade coupled to a lower end. The handles or blades were pivotally coupled to each at a single pivot point. The blades moved between a first, open position and a second, closed position that corresponded to a first and second handle position. When the blades were in the first, open position a user thrust the post hole digger toward the ground and caused the blades to bite into the ground. To maximize the force of the bite, the blades were generally perpendicular to the ground when they were in the first, open position. To further maximize the force of the bite, the handles were generally vertically aligned with the blades so that substantially all of the worker's effort (force) was directed directly through the blades and into the ground. This configuration further allowed the worker to position his/her hands and wrists in a comfortable position, generally parallel to the ground. After the blades engaged the ground, the worker moved the handles into the second position thereby causing the blades to move into the second, closed position. During this motion, the dirt is separated from the ground. The closing force acting on the blades is related to the force applied to the handles. The force applied to the handles was enhanced by the length of the lever arm created by the length of the handle. After the blades have been closed, the worker, while holding the blades in the second, closed position, lifts the post hole digger thereby removing the dirt from the hole.
The quantity of dirt held by the blades is controlled by the shape of the blades and the nature of the dirt. Typically, the blades are elongated and have an arcuate cross-sectional shape. The blades were commonly somewhat pointed and the edges were shaped so that, when the blades were in the second, closed position, the blades substantially enclosed a quantity of dirt. The shape of the blades was also related to the configuration of the pivot point and the handles. That is, for example, if the blades were spaced far apart, e.g. to engage a greater quantity of dirt, the handles would have to travel through a greater arc in order to close the blades. A greater arc requires a wider hole and more effort by the worker. Lengthening the blades would reduce the amount of travel required to close the blades, but would, in turn, reduce the relative lever arm between the blades and the handles, thus requiring a greater effort on the part of the worker.
In addition to the shape of the blades, the ease of use and usability of a post hole digger was controlled by various factors such as, but not limited to, the length and shape of the handles and the type of the pivot point. As shown in FIG. 1, the most typical configuration for a prior art post hole digger had handles 1, 2 about five to six feet in length, blade members 3, 4 about one half foot to a foot in length, and an offset pivot point 5. That is, each handle 1, 2 or blade 3, 4 had a tab 6, 7 extending toward the other handle 1, 2 or blade 3, 4 with a pivot point 5 disposed thereon. The pivot point 5, typically, had a pair of openings (not shown), one on each tab 6, 7 and a pivot pin 8. The pivot point 5 was, typically, located near the interface between the handle 1, 2 and the associated blade 3, 4. Additionally, each tab had a length of about three inches thereby providing a separation between the handles, when in the first position, of about six inches. The longitudinal axis of each handle 1, 2 is generally aligned with the longitudinal axis for the associated blade 3, 4. Each handle 1, 2 further had a hand grip portion 9 disposed near the top of each handle 1, 2. When coupled by an offset pivot point, the hand grip portion 9 of each handle 1, 2 was located on the same side of the pivot point 5 as the blade 3, 4, associated with that handle 1, 2. To close the blades 3, 4, the worker pulled the handles 1, 2, apart. To open the blades 3, 4, a worker moved the handles 1, 2 together until the handles 1, 2 were generally parallel to each other. Additionally, the handles 1, 2 or blades 3, 4, typically, had a pivot stop structured to halt the rotation of the handles 1, 2 and blades 3, 4 when the handles 1, 2 and blades 3, 4 were generally parallel. With the blades 3, 4 held in a generally parallel configuration, a worker could concentrate on the downward motion of the tool without having to position the blades 3, 4 for the bite.
An offset pivot post hole digger according to this configuration is easy to manufacture and is not too heavy; however, the range of motion of the handles is not suitable for a moderately deep hole. When the handles 1, 2 are in the second position, i.e. pulled apart, the span (width) of the tool increases as a function of the distance from the pivot point 5. As the pivot point 5 is disposed at the lower end of the handles 1, 2, essentially the entire length of one handle 1 moves away from the other handle 2. Thus, in order for the handles 1, 2 to be in the second position, the hole must be wide. Conversely, when the handles are in the first position, i.e., generally parallel, the tool is in its most narrow configuration and can be easily inserted into the hole.
A post hole digger with a traverse pivot point has a scissor-like configuration, as shown in FIG. 2, wherein pulling the handles 1A, 2A apart results in the blades 3A, 4A moving apart and, conversely, moving the handles 1A, 2A together results in the blades 3A, 4A moving together. When a traverse pivot point 5A is used, the pivot point 5A is typically located near the lower end of the handles 1A, 2A, but above the blades 3A, 4A. As shown in FIG. 2, the blades 3A, 4A are generally disposed at an angle relative to the longitudinal axis of the handles 1A, 2A so that the blades 3A, 4A may be positioned: generally perpendicular to the ground while still being separated. That is, if the blades 3A, 4A were generally aligned with the associated handles 1A, 2A and the blades 3A, 4A were in an open position, the blades 3A, 4A would not be generally perpendicular to the ground. In this configuration, the post hole digger is generally wider when the handles 1A, 2A are in the first position and more narrow when the handles 1A, 2A are in the second position; however, because the pivot point is located at a medial position on the handles 1A, 2A, the range of motion is generally smaller than on an offset pivot post hole digger.
In this configuration, a worker uses the, typically stronger, pectoral muscles to push the handles 1A, 2A together to close the blades 3A, 4A. While this could be considered an advantage, this motion is also the opposite of the motion generally associated with a post hole digger. As such, some workers do not care for a traverse pivot point post hole digger. This configuration also has a disadvantage in that, when thrusting the tool downwardly, the worker must hold the handles 1A, 2A within a generally narrow range of separation in order for the blades 3A, 4A to be maintained generally perpendicular to the ground during the bite. Moreover, the worker's hands may be in an awkward position during the thrust. That is, on a traverse pivot point post hole digger, the worker's hands are generally at an angle relative to the ground on the down stroke.
There is, therefore, a need for a post hole digger with a limited range of motion between the handle first position and handle second position.
There is a further need for a post hole digger having a traverse pivot point that is also structured to maintain the handles in a generally vertical and parallel orientation while the blades are in the first, open position.
There is a further need for such a post hole digger to have a reduced weight and size.